THE SOIL. 33 



there is a necessity for deeper soil warmth. If 

 the soil were warm to a depth of several feet in 

 early spring, before plants have time to send their 

 roots down, a great amount of valuable plant food 

 would be dissolved on account of the increased 

 temperature of the water, and hence lost. So 

 nature has provided that the soil be warmed down- 

 ward only as fast as the roots of plants can use it. 



Soil in a natural state, such as that of a forest, 

 has a most wonderful means of regulating its own 

 temperature. Covered with a thick layer of leaves 

 each autumn in our latitude, it is protected from 

 sudden changes, both on account of the noncon- 

 ducting property of the leaves themselves, and also 

 of the confined air among them. Early spring 

 plants have learned to grow there, even before the 

 frost is quite all out of the ground, and blossom 

 before the needed light for their full development 

 is shut out by the dense foliage of mid-summer. 

 Trees do not put forth their buds and leaves till the 

 last trace of frost has left the ground and air. 

 The ground is kept cold for their own good. 



Since plants do best in a warm soil, and one that 

 does not admit of too sudden changes of temper- 

 ature, it remains with the farmer to regulate the 

 conditions which govern them. As heat is taken 

 from the soil . in evaporating water at its surface, 

 it should be left in such a condition that as little 

 evaporation takes place as possible. Every unit of 

 heat spent in evaporating water leaves the s>il j-ust 



